Epitaxy is the oriented crystalline growth between two crystalline solid surfaces wherein the surface of one crystal has suitable positions for deposition of a second crystal. More typically, epitaxy refers to the growth of a crystalline layer upon a crystalline substrate. One common technique for epitaxial growth is chemical vapor deposition (CVD). In the microelectronics industry, for example, crystalline silicon is epitaxially grown upon silicon wafer substrates in a heated reactor.
As shown in FIG. 1, a conventional epitaxial reactor is a barrel reactor defining a CVD chamber in which a barrel-like holder or susceptor is mounted so as to rotate about its vertical axis. Semiconductor wafers are placed in recessed pockets defined by the susceptor so as to be held at a slight angle, such as 2.degree., from vertical. As such, the susceptor holds the wafers in a manner which permits the wafers to have maximum surface area exposure to the chemical vapor while utilizing the force of gravity to retain the wafers within the pockets. A barrel reactor also generally defines gas inlets near the top of the CVD chamber and an exhaust port near the bottom of the CVD chamber such that gas entering the CVD chamber via the gas inlets generally flows downwardly over the wafers prior to exiting the CVD chamber via the exhaust port.
Unfortunately, eddy currents are oftentimes created within conventional reactors. As known to those skilled in the art, eddy currents can cause inhomogeneous silicon deposition upon the wafer substrates during epitaxial deposition of silicon due to the uncontrolled number of passes that the gas makes over the wafers. Likewise, in instances in which the reactor is used to clean the wafers prior to the epitaxial deposition of silicon, the eddy currents also cause uneven and unpredictable etching of the wafer substrates. There is therefore a need for epitaxial barrel reactors which create fewer eddy currents in order to permit the barrel reactors to operate more reliably.